Safety valve

ABSTRACT

Safety valve, characterized in that it principally consists of a housing (1), provided with an inlet (2) and and outlet (3); a main cut off valve (4) installed in the housing (1); and means working together with the flow of liquid which with the removal of liquid and after a lapse of time shut the main cut off valve (4), which are reset in their starting position each time an equal or almost equal pressure in the liquid is created at the inlet (2) and outlet (3) of the safety valve and which when the main cut off valve (4) is shut, hold it shut as long as a well defined drop of pressure remains in existence over the main cut off valve (4), whereby these means are driven by means of a by-pass, such by means of a channel (6) that is situated apart from the main passage (5).

This invention relates to a safety valve, more especially to a valvethat is intended to be placed in pipes for liquids.

In particular the object of the invention is a safety valve forcontrolling the consumption of liquid in a network of pipes, whereby thesafety valve provides the closing of the network of pipes when anuncontrolled removal of liquid takes place. More especially theinvention concerns a valve that is closed as soon as an uninterruptedflow of liquid has existed for a well defined time.

The safety valve is in the first place intended to be placed in thesupply of the domestic water mains in order by so doing in the case ofleaking taps, leaking pipes or similar to obtain that after a lapse oftime the water mains are automatically shut off, such in order to limitwater damage and similar to a minimum.

A safety valve to control the water supply in washing machines is knownfrom the French patent application No 2.193.164 which discloses a safetyvalve in which the driving mechanism for automatically closing the valveis actuated by means of the complete flow through the valve. In this waythe displacement carried out by said driving mechanism is proportionalto the total amount of liquid which passes through the valve.

Consequently the device as disclosed in FR 2.193.164 shows thedisadvantage that the valve is shut in function of the amount of liquidpassed through the valve, but not after the lapse of a predeterminedperiod of time.

The present invention relates to a safety valve not having saiddisadvantage.

The present invention therefore has a safety valve as object, comprisinga housing provided with an inlet and an outlet; and a main cut off valveinstalled in the housing; and is characterized in that it alsocomprises, at one hand, means working together with the flow of liquidwhich with the removal of liquid and after a lapse of time shut the maincut off valve, which are reset in their starting position each time anequal or almost equal pressure in the liquid is created at the inlet andoutlet of the safety valve, such as a result of the interruption of thewater consumption, and which when the main cut off valve is shut, holdit shut as long as a well defined drop of pressure remains in existenceover the main cut off valve, whereby these means are driven by means ofby-pass, such by means of a channel that is situated apart from the mainpassage and, at the other hand, a second cut off valve place in the mainpassage which allows that an almost constant and sufficient drop ofpressure is created over the separate channel, even with a very smallremoval flow.

Preferably the by-pass consists in a channel which provides in aparallel connection over the second cut off valve.

In a preferred embodiment the aforementioned means principally consistsof a moving mechanism that after a defined stroke provides for theshutting of the main cut off valve; driving means driven by means of theaforementioned by-pass in order to move the moving mechanism; couplingmeans consisting of at least a first coupling part and a second couplingpart, which provide a coupling that can be engaged and disengagedbetween the driving means and the moving mechanism; servo-means whichengage the coupling means during the periods that a flow of liquid iscreated at the inlet; resetting means which work together with themovement means and reset the latter in a starting position, each timewhen the removal of liquid is stopped when the main cut off valve isstill opened; and the resetting means working together with the main cutoff valve which can bring the cut off valve from shut to open positionwhen the drop of pressure over the main cut off valve becomes zero oralmost zero.

In order to show better the characteristics according to the presentinvention, a preferred embodiment is described hereafter, as examplewithout any restrictive character, with reference to the encloseddrawings, in which:

FIG. 1 shows the safety valve in top view;

FIG. 2 shows a cross-section according to line II--II in FIG. 1;

FIGS. 3 and 4 show in a similar view to that from FIG. 2 the safetyvalve for different positions;

FIGS. 5 and 6 show on larger scale cross-sections according to linesV--V and VI--VI in FIG. 4;

FIGS. 7 and 8 show different positions of the part that is shown in FIG.5;

FIG. 9 shows the safety valve in a similar view to that from FIG. 2,such for yet another position.

As shown in FIG. 1, the safety valve principally consists of a housing 1provided with an inlet 2 and an outlet 3, whereby the inlet 2 isconnected to a supply source, while a distribution network for exampleis coupled to the outlet 3. The housing 1, as shown in FIG. 2, containsa main cut off valve 4 and means working together with the flow ofliquid which shut the main cut off valve 4 with the removal of liquidand after a lapse of time, which are reset in their starting positioneach time when an equal or almost equal pressure is created in theliquid at the inlet 2 and the outlet 3 of the safety valve and whichwhen the main cut off valve 4 is shut, hold it shut as long as a welldefined drop of pressure remains in existence over this main cut offvalve 4, whereby these means are driven by means of a by-pass through achannel 6 separate from the main passage 5.

The latter means principally consist of a moving mechanism 7 that aftera defined stroke provides for the shutting of the main cut off valve 4;driving means 8 driven by means of the aforementioned by-pass in orderto move the moving mechanism 7; coupling means 9 consisting of at leasta first coupling part 10 and a second coupling part 11, which provide acoupling that can be engaged and disengaged between the driving means 8and the moving mechanism 7; servo-means 12 which engage the couplingmeans 9 during the periods that a flow of liquid is created at the inlet2 or outlet 3; resetting means 13 which work together with the movementmeans 7 and reset the latter in a starting position each time when theremoval of liquid is stopped when the main cut off valve 4 is stillopened; and the resetting means 14 working together with the main cutoff valve 4 which can bring the main cut off valve from shut to openposition when the drop of pressure over the main cut off valve becomeszero or almost zero.

In the embodiment shown in the figures the moving mechanism 7principally consists of a rotatable element 15, that, as is stillfurther explained in the description, with the engaging of the couplingmeans 9 is moved by the driving means 8, as well as a guiding mechanism16 working together with the main cut off valve 4 and the rotatableelement 15 that in a well defined angular position allows the axialmovement of the main cut off valve 4 situated in a radial plane, all ofwhich such that this valve is pushed onto its seat 17 by the flow ofliquid and whether or not with assistance of electric means as yetfurther described. The rotatable element 15 principally consists of acylinder which is connected to the main cut off valve 4 or, as shown inFIG. 2, is produced with this in one piece.

The aforementioned guiding mechanism 16 is composed of at least onesupport in the form of a lip 18 rotating with the rotatable element 15;a circular guide 20 in the form of a collar or similar on which the lip18 rests and can slide over, situated in a radial plane in relation tothe axial axis 19 of the valve; and at least one axial notch 21installed in the guide 20, such that with the rotation of the rotatableelement 15 and the lip 18 rotating with this, the latter can be broughtinto a position whereby it is opposite the notch 21, through which thelip 18 engages with the notch 21 and the main cut off valve 4 can bepushed into its seat 17.

The safety valve preferably also shows a flow rupture safety device, inother words a safety device which allows that at any moment with anexcessively large removal flow the main cut off valve 4 is automaticallyshut. For this purpose the aforementioned lip 18 is part of a part 22axially movable in relation to the rotatable element 15. The part 22 isslidable over for example a hexagonal guide 23 provided on the rotatableelement 15, whereby the part 22 in a farthest undepressed position, ispushed against a stop 24 by means of a compression spring 25 installedaround the hexagonal guide 23. The precise operation of the unit isfurther described hereafter.

The resetting means 13 which can reset the moving mechanism into thestarting position, principally consist of a torsion spring 26 whichforces the rotatable element 15 into a well defined sense of rotation,whereby the movement is limited by means of a stop 27 against which therotatable element 15 makes contact, for example by means of a lip 28 orany other support provided hereon. The stop 27 is preferably movable. Itis clear that because of this the length of the stroke of the lip 18over the guide 20 can be altered before this lip 18 is placed oppositethe notch 21. In order to be able to move the stop 27, in the embodimentshown in the figures it is installed on a rotatable regulating element29 of which the desired angular position can be adjusted by means ofadjusting means 30. The regulating element 29 hereby consists of acylinder which is situated around the rotatable element 15. The stop 27is for example formed by a protrusion in the form of a rod present onthe inside of the cylinder. The adjusting means 30 are formed by ashaft, rotatable for example by means of a hexagonal key, which has atoothing 31 on its circumference which meshes with a rim gear 32provided on the circumference of the rotatable regulating element 29,such that through the rotation of the adjusting means 30 the position ofthe stop 27 can be chosen. It is clear that the adjusting means 30and/or the rotatable regulating element 29 provide for a sufficientlyself restraining operation, such that with the driving of the rotatableelement 15 the rotatable regulating element 29 is not taken along by theforce of the torsion spring 26. It is observed that the torsion springis preferably attached by its extremities between on the one hand therotatable element 15, and on the other hand the rotatable regulatingelement 29.

In the embodiment shown both the coupling parts 10 and 11 of thecoupling means 9 stand axially disposed in each others prolongation. Ontheir sides directed toward each other they are equipped with toothingsin the form of a rim gear, respectively 33 and 34. The first couplingpart 10 shows a cylindrical part 35 on which there is a toothing viawhich the driving of the driving means 8 occurs. The first coupling part10 can be moved axially toward the second coupling part 11 by means ofthe servo-means 12, whereby the toothings 33-34 them mesh with eachother. The second coupling part 11 is connected to the rotatable element15 or, as shown in FIG. 2, forms one unit with this. FIG. 3 shows themeshing in the coupled position.

The driving means 8 principally consist of a turbine 37, placed in theaforementioned by-pass, which is coupled via several transmissions,formed by worm and toothed wheels 38 through 41, to the first couplingpart 10, more especially to the toothing 36. The first worm wheel 38 ismounted on the shaft 42 of the turbine 37. The worm and toothed wheeltransmissions permit very great transmission ratios. Preferably atransmission ratio of at least 1/3.000 is realised, while in a practicalembodiment this preferably amounts to 1/30.000, which means that theturbine has to make 30.000 revolutions in order to rotate the couplingpart 10 one revolution.

It is clear that the channel 6 exits tangentially in the chamber of theturbine 37. The liquid leaves the turbine along a passage 43 which isaround the shaft 42, but can also according to a variant, as with asingle jet water meter, flow out on the opposite side of the inlet.

In the embodiment shown the aforementioned servo-means 12 consist of acut off valve 44 placed in the inlet 2, which by means of a relativelylight spring 45 is forced against the direction of flow of the liquidtoward its closed position. The cut off valve 44 is connected to thefirst coupling part 10 by means of a connection 46. The force of thespring 45 is so selected that the cut off valve 44 opens with theslightest difference in pressure and the first coupling part 10 coupleswith the second coupling part 11.

The connection 46 is telescopically collapsible and shows stop formingmeans 47, such as a collar, as well as elastic means, such as acompression spring 48, which push the first coupling part 10 and the cutoff valve 44 to a maximum position from each other, whereby in thisposition and when the cut off valve 44 is shut, thus as in FIG. 2, thefirst coupling part 10 is just not coupled to the second coupling part11. The telescopic connection 46 permits that, on the one hand, onlylimited movement of the first coupling part 10 is necessary in order toengage the coupling means 9 and on the other hand, after the engagementof the coupling means 9 the valve 44 can still further open, such by thedepression of the spring 48.

The spring 48 also has the function of providing that in depressedposition and with putting the lip 18 and the notch 21 opposite eachother the main cut off valve 4 can also already be pushed shut by verysmall flows, such that for the shutting of the main cut off valve 4 noflow of well defined volume is required.

The inlet 49 of the channel 6 is, as is schematically shown in FIG. 2,downstream from the cut off valve 44, but upstream from the main cut offvalve 4. This offers the advantage that with the removal of liquid firstthe coupling means 9 are engaged by means of the cut off valve 44, onlyafter which liquid can flow through the channel 6 and the turbine 37 canbe driven.

In FIG. 2 the channel 6 is only schematically denoted. The preciselocation of this is shown more clearly in FIG. 1.

In order to obtain that already the slightest flow of liquid wouldprovide for the driving of the turbine 37, the safety valve shows asecond cut off valve 50 which is placed in the main passage 5,downstream from the seat of the aforementioned cut off valve 44. The cutoff valve 50 is forced into the closed position by means of a spring 51and only opens with a sufficiently great difference in pressure. Theinlet 49 of the channel 6 is situated between the respective seats ofthe two cut off valves 44 and 50, such that with a limited flow ofliquid the liquid only flow through the channel 6, while with a greaterflow of liquid and a greater difference in pressure the cut off valve 50opens and the liquid flows both through the main passage 5 and throughthe channel 6. The cut off valves 44 and 50 perferably each consist ofcylindrical bodies which are axially slidable along each other, wherebya mutual sealing is provided in the form of a supple bendable seal 52 orrolling membrane.

The aforementioned resetting means 14 principally consist of acompression spring 33 which can open the main cut off valve 4 when thedifference in pressure of the pressures along both sides of the latteris almost zero, but in its farthest position does not necessarily couplethe main out off valve 4 and more especially the second coupling part11, to the first coupling part 10. In order to obtain the latter, theexpansion of the compression spring 53 is limited to a well definedlength, such by stop forming elements 54, 55 and 56. In order to keepthe friction between the resetting means 14 and the rotatable element 15to a minimum the contact zone 57 between the element 54 and the part 22is limited to a minimum, almost to a point contact.

The safety valve preferably also shows means which permit a new buildupof pressure. In the embodiment shown according to FIG. 2 these meansconsist of a connecting channel 58 that connects the spaces before andafter the main cut off valve 4, as well as means installed herein inorder to regulate the passage, for example an adjusting screw 59 whichby screwing in, respectively screwing out shuts off the connectingchannel to a greater or lesser degree.

The operation of the safety valve can be deducted from the FIGS. 2through 9 and is as described hereafter. FIG. 2 shows the safety valvein condition of rest. With the removal of water from the network ofpipes connected to the outlet 3 the pressure at the outlet 3 and thusalso behind the cut off valve 44 becomes less than at the inlet 2.Because of this, as shown in FIG. 3, the cut off valve 44, whichfunctions as switch valve, is moved, through which the first couplingpart 10 meshes with the second coupling part 11. From that moment theliquid can already flow via the channel 6 through the turbine 37 throughwhich this begins to rotate. When sufficient liquid is requested at theoutlet 3 and consequently a sufficiently large drop in pressure ispresent before and after the cut off valve 50, the latter is alsoopened, so that a condition arises, as shown in FIG. 4. At that moment anormal through flow is realised whereby the liquid flows from the inlet2 via the main passage 5 toward the outlet 3 and whereby a small part ofthe liquid keeps flowing through the channel 6 with almost a constantflow, since by opening the cut off valve 50, the drop in pressure overthe inlet and outlet of the channel 6 is maintained almost constant.

The driven turbine then ensures that the first coupling part 10 isrotated around its axis via the worm and toothed wheels 38 through 41,that in its turn takes along in its rotating movement the secondcoupling part 11 and the rotatable element 15. The rotatable element 15is then rotated against the force of the torsion spring 26, whereby thepart 22 with the lip 18 slides over the guide 20. The lip 28 herebycomes loose from the stop 27.

In the FIGS. 2 through 4 a starting position is shown whereby as furtherclarified in FIG. 5 the part 22 must follow an angle A of 180 degreesbefore the lip 18 is placed opposite the notch 21. In FIG. 6 it is shownin detail how the lip 28 of the rotatable element 15 makes contact inthe starting position with the stop 27 of the regulating element 29adjustable according to arrow P.

It is clear that by the movement of the rotatable regulating element 29,such by means of the adjusting means 30, the stop 27 can be situated indifferent positions, through which the lip 18 can then also take on adifferent starting position in relation to the notch 21. In FIG. 7 astarting position is shown whereby the rotatable element 15 and the part22 connected herewith as well as the lip 18 must first follow an angle Aof almost 360 degrees before the lip 18 is brought opposite the notch21. FIG. 8 shows another adjustment whereby the angle A amounts to aminimum. The minimum and maximum adjustment is determined by a stop 60which is included in the rim gear 32 and with the minimum or maximumposition, either along one side or along the other side comes intocontact with the rotatable shaft 30.

When for a well defined period an uninterrupted flow of liquid remainsin existence, after a defined time the lip 18 is placed opposite thenotch 21, with the result that the main cut off valve 4 can move axiallyand be closed either by the action of the flow of liquid, or under theinfluence of the spring 48 in the case of small through flows when thedrop in pressure over the cut off valve 4 thus contributes little ornothing to the movement of the main cut off valve 4 against the force ofthe spring 53. The lip 18 hereby enters into the notch 21. This positionis shown in FIG. 9. The connection via the coupling parts 10 and 11remains in existence under the influence of the force exerted by thespring 48 against the force of the spring 53, until the last moment thatthere is through flow of liquid. Immediately after the shutting of themain cut off valve 4 the pressures before and after the cut off valve 44and 50 become equal, through which these valves are closed by means oftheir springs. As a result of this the first coupling part 10 isuncoupled from the second coupling part 11 via the connection 46 andwith the help of the stop forming means 47.

In order to open the main cut off valve 4 again, a buildup of pressuremust again be realised at the outlet 3 which is equal or almost equal tothe pressure in the liquid at the inlet 2, such that the resetting means14 can again bring the main cut off valve 4 into opened position. Thisbuildup of pressure is realised because a very limited amount of watercan come via the connecting channel 58 from before the main cut offvalve 4 to after the main cut off valve, whereby it is then requiredthat the network of pipes or similar connected to the outlet 3 is againclosed. In that case this network of pipes is partially filled until thebuildup of pressure is realised whereby the main cut off valve 4 isopened.

In the case that the network of pipes connected to the outlet 3 isalready sealed off before the lip 18 has reached the notch 21, themoving mechanism 7 is replaced in the starting position, such because inthat case due to the equal pressure before and after the cut off valves44 and 50 the latter are closed, through which the first coupling part10 is pulled loose from the second coupling part 11 and the rotatableelement 15 is rotated back by means of the torsion spring 26 such untilthe lip 28 rests against the stop 27.

The use of a separate channel 6 for driving has as advantage that arelatively small and very precise regulating and measuring element, suchas the turbine 37, can be applied with a high starting sensitivity, sothat very limited consumptions of liquid can also be measured.Furthermore the power will be almost independent of the size of thetotal flow that flows through the safety valve, since--as alreadyclarified earlier--the through flow through the channel 6 and throughthe turbine 37 is maintained almost constant. In so doing it is obtainedthat the movement of the lip 18 is principally proportional to theperiod of time during which a flow of liquid, irrespective whether largeor small, remains in existence through the safety valve 1. By theregulation of the adjusting means 30, and the shifting of the stop 27between the minimum and maximum position, in practise a regulation isthen also possible between a period of approximately one hour, maximum,to two minutes, minimum.

The safety valve according to the invention offers the advantage thatwith the protracted opening of a tap, connected to the outlet 3, themain cut off valve 4 shuts, but can easily be opened again by closingthe tap again for a while until a new buildup is realised at the outlet.In the case of a burst pipe or similar the safety valve forms a safetydevice, which effects an automatic shut off, with exception of thepossible very minimal flow of liquid through the connecting channel 58.

When a pipe rupture or similar occurs before the outlet 3, the drop ofpressure over the main cut off valve 4 becomes so great that this isclosed against the force of the compression spring 25 irrespective ofthe position of the part 22.

From the figures it is clear that, in order that the safety valve mayfunction well, the spring 51 is so selected that the cut off valve 50remains shut until a drop in pressure is created which is sufficientlygreat to engage the coupling means 9 and to deliver a force which allowsthe main cut off valve to close against the force of its resetting means14. Furthermore the elastic means 48 must deliver a greater tension thanthe resetting means 14 of the main cut off valve 4.

It is clear that the safety valve can also function as limiter in orderto prevent that for a predetermined time specific amounts of water aretaken, whereby the adjusting screw 59 can be screwed in completely sothat the connecting channel 58 is closed, and this adjusting screw issealed, such that the main cut off valve 4 can only be opened again byan authorised person.

The present invention is in no way restricted to the embodimentsdescribed as examples and shown in the figures, but such safety valvecan be implemented in all kinds of forms and dimensions withoutdeparting from the scope of the present invention.

I claim:
 1. A safety valve, comprising:a housing having an inlet, anoutlet, a main passage, and a bypass channel; a main cut-off valveinstalled in the housing; means, actuated by the flow of liquid withinthe safety valve, for moving the main cut-off valve into a closedposition after a predetermined period of time has lapsed and for holdingthe main cut-off valve in the closed position when a pressure dropexists across the main cut off valve, the moving and holding means beingreset to a starting position each time a first pressure on liquid at theinlet and a second pressure on liquid at the outlet are approximatelyequal and including a moving mechanism which after moving a specificstroke distance closes the main cut-off valve, driving means, disposedin the bypass channel, for driving the moving mechanism first resettingmeans for moving the moving mechanism into the starting position eachtime the main cut off valve is in an open position and liquid is notbeing removed from the safety valve; second resetting means for movingthe main cut-off valve from the closed position to the open positionwhen the pressure drop across the main cut off valve is approximatelyzero; a second cut-off valve disposed in the main passage which ensuresthat a substantially constant drop of pressure is created across thebypass channel; a coupler having first and second coupling parts whichcan be engaged and disengaged with each other, the coupler beingconnected to the driving means and the moving mechanism; and a servodevice which engages with the coupler when a flow of liquid is createdat the inlet such that when the first and second coupling parts are notengaged the first resetting means are set into operation.
 2. A safetyvalve according to claim 1, further comprising means for allowing a newbuildup of pressure behind the main cut-off valve after the main cut-offvalve is in the closed position.
 3. A safety valve according to claim 2,wherein the means for allowing the new buildup of pressure includes aconnecting channel that connects a first space located before the maincut-off valve with a second space located after the main cut-off valve.4. A safety valve according to claim 3, wherein the connecting channelincludes means for regulating the flow of liquid therethrough.
 5. Asafety valve according to claim 4, wherein the means for regulating theflow includes an adjusting screw which can be screwed to regulate theflow of liquid through the connecting channel.
 6. A safety valveaccording to claim 1, wherein the moving mechanism includes a rotatableelement that engages with the coupler and is moved by the driving means,and a guiding mechanism cooperating with the main cut-off valve and therotatable element such that when the guiding mechanism is moved over adefined angular distance, the main cut-off valve can move from the openposition to the closed position.
 7. A safety valve according to claim 6,wherein the rotatable element is connected to the main cut-off valve oris integrally produced with the main cut-off valve as a single piece. 8.A safety valve according to claim 6, wherein the guiding mechanismincludes a lip which rotates with the rotatable element and a circularguide on which the lip rests and slides over, and wherein the circularguide has an axial notch such that when the lip enters the axial notch,the main cut-off valve is in the closed position.
 9. A safety valveaccording to claim 6, further comprising a stop which determines thestarting position of the rotatable element.
 10. A safety valve accordingto claim 9, wherein the stop is movable, and further comprising meansfor adjusting a position of the stop.
 11. A safety valve according toclaim 10, further comprising a regulating element which is rotatablearound the rotatable element, the regulating element including the stop.12. A safety valve according to claim 11, wherein the regulating elementfurther includes a rim gear and the adjusting means includes a rotatableshaft having teething thereon, the teething meshing with the rim gear.13. A safety valve according to claim 6, wherein the first resettingmeans includes a torsion spring.
 14. A safety valve according to claim1, wherein the first and second coupling parts have first and secondteething, respectively, the first and second teething meshing with eachother.
 15. A safety valve according to claim 6, wherein the first andsecond coupling parts have first and second teething, respectively, andthe first and second teething can mesh with each other, and wherein thefirst coupling part is driven in a rotating manner by the driving meansand the second coupling part is an integral part of or is connected tothe rotatable element.
 16. A safety valve according to claim 15, whereinthe first and second coupling parts are rotatable along a common axis,and the first coupling part is movable along the common axis by theservo device, such that the first coupling part engages with the secondcoupling part.
 17. A safety valve according to claim 15, wherein thedriving means includes a turbine which is disposed in the bypass andwhich is coupled to the first coupling part.
 18. A safety valveaccording to claim 17, wherein the first coupling part and the turbineare connected to each other via a plurality of worm and toothed wheeltransmissions.
 19. A safety valve according to claim 18, wherein theplurality of worm and toothed wheel transmissions create an overalltransmission ratio of at least 1/3.000.
 20. A safety valve according toclaim 19, wherein the servo device includes an axially movable cut-offvalve disposed in the inlet, and wherein the axially movable cut-offvalve, when in an open position couples the first coupling part to thesecond coupling part, and the axially movable cut-off valve is forcedinto its closed position by means of a spring and is in its openposition when a predetermined small pressure difference exists acrossthe axially movable cut-off valve.
 21. A safety valve according to claim20, wherein the first coupling part and the axially movable cut offvalve are axially disposed in relation to each other and are connectedto each other by a telescopically collapsible connection, thecollapsible connection having a stop and an elastic part which pushapart the first coupling part and the axially movable cut-off valve intoa maximum extended position such that in a position of rest the firstcoupling part is located in front of and does not engage with the secondcoupling part, and wherein when the first and second coupling partsengage each other, the axially movable cut off valve can still openagainst the force of the elastic part.
 22. A safety valve according toclaim 21, wherein the bypass channel has an inlet which faces toward theturbine and which is located downstream from a seat of the axiallymovable cut-off valve and upstream from a seat of the main cut-offvalve.
 23. A safety valve according to claim 20, wherein the secondcut-off valve is disposed in the main passage downstream from theaxially movable cut-off valve and is held in a closed position by aspring, and wherein when liquid is removed from the safety valve thesecond cut-off valve is opened by the pressure of liquid, and the inletof the bypass channel begins in a space which is situated between theseat of the axially movable cut-off valve and the seat of the secondcut-off valve.
 24. A safety valve according to claim 23, wherein thespring keeps the second cut off valve in its closed position until apredetermined drop in pressure is created which causes the first andsecond coupling parts to engage and which delivers a first force thatallows the main cut-off valve to move to its closed position against asecond force of the second resetting means.
 25. A safety valve accordingto claim 22, wherein the elastic part creates a first force which isgreater than a second force created by the second resetting means.
 26. Asafety valve according to claim 23, wherein the axially movable andsecond cut-off valves are mounted concentrically, and further comprisinga supple, pliable seal which is disposed between the axially movablecut-off valve and the second valve cut-off valve.
 27. A safety valveaccording to claim 26, wherein the second resetting means includes aspring which exerts a comprehensive force on the main cut-off valve, ina direction opposite to a direction of the flow of liquid.
 28. A safetyvalve according to claim 1, further comprising a flow rupture safetydevice disposed between the main cut-off valve and the guidingmechanism.
 29. A safety valve according to claim 6, wherein the safetyvalve further comprise a flow rupture safety device including a couplingdisposed between the main cut-off valve and the guiding mechansim, thecoupling allowing a movement of the main cut-off valve up to its seat,and a flow rupture spring mounted in the coupling which only allows themovement of the main cut-off valve with respect to the guiding mechanismwhen a predetermined high difference in pressure over the main cut-offvalve exists.